Large and complex refrigeration systems are required to provide air-conditioning in large office buildings, to maintain the large storages of food at low temperatures in large warehouses, and to provide relatively low-temperature environments in other applications (e.g., pharmaceutical manufacturing). These refrigeration systems are typically closed-cycle refrigeration systems incorporating a plurality of components that cycle a refrigerant through alternate stages of compression and expansion. In some parts of the refrigeration system, the refrigerant is in a liquid state; and in other parts of the system the refrigerant is a gaseous form. The refrigeration system compressor or compressors operate to pressurize the gaseous refrigerant in the “high-pressure side” of the system. The pressure in the system pipes and other equipment on the high-pressure side can be considerably more than the outside or ambient pressure. Because these systems store and utilize fluids (i.e., gases and liquids) at relatively high-pressure, leaks and ruptures have long been concerns with such systems. Other industrial systems, including industrial boiler systems, also include closed systems that have high-pressure vessels and pipes. Such systems are generally referred to herein as “closed pressurized systems.”
Ammonia is commonly used as a refrigerant in closed-cycle refrigeration systems, due to its excellent heat transferring properties, availability and low cost for large commercial operations, such as food and beverage manufacturers and distributors, pharmaceutical manufacturers, air conditioning systems for large buildings, and in electrical power generation plants. However, ammonia gas can be toxic at relatively low concentrations. Ammonia is also a moderate fire risk and is explosive when mixed with air in the 16%-25% range. In closed refrigeration systems the continuous cycle of expansion and compression of the gaseous ammonia creates a risk that the ammonia may breach the system, resulting in the escape of toxic gas. Thus, a rupture of the system could have calamitous results. Consequently, there is a need to prevent ammonia leaks in facilities using such refrigeration systems.
In large refrigeration systems, a plurality of vessels, pipes, and other components located down stream of compressors and other equipment that produce highly pressurized fluids, store and/or carry the highly pressurized fluids. In order to prevent ruptures and explosions, these vessels, pipes, and other components may each be outfitted with a pressure relief system that includes pressure relief valves to protect the components from excessive pressure. The pressure relief systems are critical components in the safety of a closed pressurized system, such as ammonia refrigeration system. The pressure relief systems maintain safe pressure levels within the system. If an abnormally high pressure occurs, a pressure relief valve will open to relieve the excess pressure, preventing potential damage to equipment and injury to personnel. Generally, the pressure relief valves will vent to the atmosphere excessive overpressure and then reseat to minimize loss of refrigerant.
Such relief valves are usually part of a pressure relief system, which may be connected to a particular pressurized vessel, pipe, or other structure containing pressurized fluid in an industrial closed-cycle refrigeration system. Industrial refrigeration systems usually include multiple pressurized structures each outfitted with a pressure relief system, and each pressure relief system may have a vent pipe that connects with a collective exhaust manifold leading to a single main exhaust pipe for releasing exhausted gas into the atmosphere. The pressure relief valves are installed in dual array arrangements in each of the pressure relief systems and are connected to a manifold within the pressure relief system which connects to the vent pipe within the pressure relief system. Such safety valve designs may include a frangible diaphragm or rupture disk upstream of each pressure relief valve. The dual arrangement of the relief valves permit one safety valve to be isolated, removed, serviced, and replaced while a second safety valve is connected to the refrigeration system so as to provide the necessary safety to operate the system. In the event of the opening of one or more of such safety valves, it has been the general practice for the operator to manually check each valve to determine where the failure occurred. This practice is not only time-consuming, but may also require that the entire refrigeration system be shut down so that each check valve may be inspected.
Pressure safety procedures in conventional ammonia refrigeration systems and other closed pressurized systems are inefficient because they utilize indicators for pressure events (e.g., rupture disk indicators) that require dismantling of the vent pipe system in order to access the ruptured disk. Such systems are also inefficient because the operator must examine each pressure relief valve system to identify where a pressure event occurred. Thus, there is a need for an improved pressure event indicator system for pressure release events in closed pressurized systems.